An electric motor is provided with windings which are wound in slot parts configured with teeth and a yoke, via electric insulator having a high dielectric constant. This configuration allows a leakage current to flow between the slot parts grounded and the windings subjected to an electric voltage.
Conventionally, a reciprocating compressor equipped with an electric motor of this type has been configured in the following manner, as disclosed in Japanese Patent Unexamined Publication No. H08-107642. That is, the motor has the slots configured with the teeth and the yoke. The whole of the inside surfaces of the slots are provided with a plurality of fine asperities. The plurality of the fine asperities yields gaps having a low dielectric constant, which allows a reduced leakage current.
However, the presence of a plurality of such the recesses in portions where a magnetic flux density is high, especially in the teeth portions, causes an increase in iron loss and a decrease in torque constant due to saturation of the magnetic flux, which results in a reduced efficiency of the electric motor. This has been a problem.